1. Field of the Invention
The present invention relates to gas discharge lamp apparatus and methods as well as to power distribution systems and processes useful in association with such lamps although the power distribution feature is not necessarily limited to the discharge lamp application. More particularly, the present invention relates to fluorescent lamps, mercury vapor lamps, sodium or metal halide lamps, as well as to other electronic loads. This invention is especially useful for lighting systems and power distribution associated with such lighting systems.
2. Description of the Prior Art
Contemporary lighting systems distribute power, such as at 60 Hertz, 115 volts RMS (or 220 volts RMS), to a variety of fixtures containing gas discharge lamps. Within each fixture is a solid state ballast which functions as an electronic controller to filter and convert the A.C. power to direct current. The D.C. is next converted to a sinusoidal source, such as 20 kilohertz, to provide operating power to the lamps. Examples of prior art ballast circuits for fluorescent lamps are shown in U.S. Pat. Nos. 3,753,071 by Engel et al; 4,109,307 by Knoll; and 4,259,614 by Kohler, as well in the Patent Cooperation Treaty Publication WO 91/16802 by Smallwood et al.
Distributed power systems for fluorescent lamps are known in the prior art, such as in U.S. Pat. Nos. 4,508,996 by Clegg et al and 5,047,696 by Nilssen. Clegg et al show D.C. driver inverters for producing high frequency signals for driving clusters of lamps. Nilssen converts primary line power to D.C., and then to 30 kHz in an inverter for parallel distribution to a plurality of light units. Power is coupled through a passive auto-transformer network to drive fluorescent light bulbs in pairs. The Clegg et al patent employs resonant circuits.
The prior art power distribution system for use in mines includes power units employing a signal at 30 kHz to drive a plurality of lamps, such as in British Patent 1,401,628. U.S. Pat. No. 4,293,799 by Roberts column 1, lines 32-42, describes the prior art to their patent as including a system wherein a plurality of "intrinsic safety" mine lamps are powered by a common power unit in a manner suggested by the aforementioned British patent. The Roberts patent shows a master unit driving a plurality of parallel connected slave units, and alleges its contribution is an improvement to such a system in the form of voltage control elements in-line between the master oscillator and the slave type units to reduce the prospect of sparking. That is, the Roberts patent includes a voltage controller between the power source and the series circuit, including the primary winding of a transformer for limiting the amount of power to a level below that which is "incendive to the atmosphere" for mine safety.
Various prior art has addressed modification of lamp envelopes to include different components. For instance, U.S. Pat. No. 4,571,526 by Wesselink shows a mercury vapor lamp configured with the discharge elements surrounding the ballast as a sealed unit. A special heat conductive thin-walled member is included for the ballast. U.S. Pat. No. 3,549,941 by Friedmann shows fluorescent lamps having starter elements, a relay and operational elements all within the lamp envelope.
U.S. Pat. No. 4,316,121 by Hammer et al also shows a lamp ballast and fluorescent bulb packaging unit. It utilizes an inductive-resistive element formed as an elongated coil parallel to the lamp tube. U.S. Pat. No. 4,857,806 by Nilssen is another form of folded lamp with ballasting circuitry in the base so it can accommodate screwing into a standard socket.
Each ballast must ensure low electromagnetic radiation, must reduce conducted noise reflected into the main power line from its internal electronics, and ideally should present as near as possible a unity power factor to the main A.C. power mains.
The contemporary fluorescent lamp ballasts typically contain rectifiers, capacitors, transistors, integrated circuits and transformers to accomplish the power conversion function. Each ballast may contain in excess of forty individual components. While a single ballast may power from one to four or more gas discharge lamps at one time, for large distributed lighting requirements in factories and department stores, for instance, thousands of these controllers are required.